INCREASED ASYMMETRIES IN 2-DEOXYGLUCOSE UPTAKE IN THE BRAIN OF FREELYMOVING CONGENITALLY ACALLOSAL MICE

To investigate the role of the corpus callosum in the expression of fu nctional brain asymmetries, we compared left and right uptake of [C-14 ]2-deoxyglucose in 43 brain regions measured in 10 C57Bl/6 mice with a normal corpus callosum and in 12 congenitally acallosal mice, after 4 5 min of free activity in a novel, large open-field arena. The metabol ic patterns across the brain appeared to be similar in the two groups of mice, as well as the average direction of asymmetry in tracer incor poration, which was higher at right in most of the brain regions for b oth acallosals and controls. However, the direction of the metabolic a symmetries of any given region was not consistent across individual an imals. The largest asymmetries were found in the central auditory nucl ei in both groups of mice, with extreme values in some acallosals. Sig nificantly larger asymmetries were found in acallosal mice for the bra in and the cortex as a whole, as weil as for the lateral geniculate an d prerectal nuclei, the olfactory tubercles, and retrosplenial, infrar hinal and perirhinal cortices. The metabolic asymmetries of the thalam ic sensory nuclei were correlated with the asymmetries of the correspo nding sensory cortical fields in the acallosal, but not in control mic e. On the other hand, asymmetries of the cortical regions were largely intercorrelated in control mice, resulting in a general activation of one hemisphere over the other, while in acallosals they were more ind ependent, resulting in a ''patchy'' pattern of cortical asymmetries. T hese results suggest that callosal agenesis; combined with the occurre nce of ipsilateral Probst bundles, leads to a loss of co-ordination in the activation of different sensory and motor areas. The impaired co- ordination might then be distributed through cortico-subcortical loops , resulting in larger asymmetries throughout the brain. Thus, a normal corpus callosum appears to balance and synchronize metabolic brain ac tivity, perhaps by smoothing the effects of asymmetrically activated a scending systems. (C) 1998 IBRO. Published by Elsevier Science Ltd.